Falcon 9 launches every three days. It's not even fully reusable and it burns kerolox, requiring the engine be cleaned.
I doubt they'll have that cadence ready for Starship within NASA's ambitious timeframe, but if they can get orbital refuelling and full reuse working (which are big ifs) high cadence should only be a matter of time. And when you're just refueling it every flight, rather than building a bespoke new rocket (as with SLS), the cost for twelve launches would likely be significantly lower than one SLS launch.
The internal cost for a Falcon 9 is approximately 15 million, and that's including a thrown away second stage, drone ship usage, fairing recovery, and engine refurbishment.
